France's Interior Minister Gerald Darmanin has described a knife attack near the former editorial offices of satirical magazine Charlie Hebdo as an "Islamist act of terrorism."
There is little doubt that it is another "bloody attack" on the country, the minister said on French television.
Darmanin said he had asked the police to look into whether the threat of terrorist acts being carried out on the streets of France had been underestimated.
The French news agency AFP also reported five further arrests, citing judicial circles. The suspects, all of whom were men, were arrested during a raid on an apartment in Pantin near Paris.
Two suspects had been detained earlier, one near the Place de la Bastille and the other in the area of the Richard-Lenoir metro station near the crime scene, several French media reported.
There are now seven suspects in police custody.
The attacks, which took place around noon on the street Rue Nicolas Appert, left two journalists injured, French Prime Minister Jean Castex told the press, adding that the victims' lives are not in danger.
Both victims were employees of Premieres Lignes, a production company, which had helped produce a documentary about the attacks on Charlie Hebdo's editorial team titled "Three Days Of Terror: The Charlie Hebdo Attacks."
The documentary, in which witnesses, police officers and survivors speak about the series of terrorist attacks in January 2015, was produced for the US broadcaster HBO, the BBC and French broadcaster France 2.
A police officer stands guard as firefighters lift an injured person into an ambulance. Photo: Alain Jocard/dpa.
The attack was prompted by caricatures of the Muslim prophet Mohammed that Charlie Hebdo published and which were deemed offensive in large parts of the Muslim world.
A trial is under way in Paris for 14 people who allegedly provided aid to the attackers who stormed Charlie Hebdo's offices on January 7, 2015, leaving 12 dead. In all, 17 people died at the hands of three attackers during a week of terror in the city.
The publication recently reprinted the caricatures and has once again been receiving threats.
The office of Premieres Lignes is in the immediate vicinity of the former Charlie Hebdo editorial office, which moved to a secret location after the attack.
One of the agency's bosses, Luc Hermann, told broadcaster BFM TV that Friday's attack was very traumatic for his company but also for all companies in the building.
He heard screams in the street, so he and other staff locked themselves in, he added.
The stabbing victims are a man and a woman, Hermann said, adding that they are "committed and remarkable employees."
One of those detained is the main suspect, according to the public prosecutor's office, an 18-year-old who was born in Pakistan.
There was a raid in Val-d'Oise in the greater Paris area, according to Franceinfo channel, which reported that the main suspect had been living there.
It was not clear what motivated the attack, though anti-terrorism investigators said they have taken over the investigation.
An armed French policeman deploys at the scene of the knife attack. Photo: Andreina Flores/dpa.
Neighbourhood blocked off
Police had earlier urged residents of the city's 11th district to stay indoors. A reporter who attempted to reach the scene found the entire neighbourhood blocked off with police tape.
Meanwhile, Castex said he had called a crisis meeting and emphasized his determination to fight terrorism.
Speaking at the crime scene, he spoke of a "symbolic place" and expressed his solidarity with the victims' families and all their colleagues.
The Charlie Hebdo editorial staff also expressed their sympathy, saying: "The entire Charlie team supports its former neighbours and colleagues and is in solidarity with them."
European Council President Charles Michel condemned the attack and expressed his solidarity with the French people.
"All my thoughts go to the victims of this cowardly act of violence," he wrote on Twitter. "Terror does not have any place on European territory."
Words of sympathy also came from Italy.
"Solidarity with #France for the vile attack near the former offices of #CharlieHebdo. We are close to the French people and we are following events with concern. Italy stands alongside those who fight against all forms of violence," Italian Prime Minister Giuseppe Conte said in a tweet.
In France, the risk of terror attacks is still assessed as very high.